A solar photovoltaic (PV) array is a parallel arrangement of strings of series-connected PV panels. A string in the context of PV arrays, often referred to simply as a “PV string,” is an arrangement of PV panels connected together in series to produce a voltage at a desired level for a downstream DC-to-AC inverter. As will be appreciated, solar PV arrays can occupy extensive surface areas. A typical PV system might contain multiple PV arrays and dozens or even hundreds of PV panels.
A PV array is composed of multiple strings of PV panels. Each string output is received in a device called a combiner, which “combines” the currents from multiple strings into a larger conductor, called a busbar, for feeding downstream equipment and ultimately to a DC-to-AC inverter that converts the DC currents produced by the strings of PV panels into an AC current. The combiner can receive strings from multiple PV arrays.
In the combiner, which typically takes the form of an enclosure referred to as a “string combiner box,” protection devices such as circuit breakers or fuses are used to limit backfeeding current from one or more strings into another string. Backfeeding current into a PV panel can damage the wiring panel or otherwise adversely affect the performance of the PV array.
Both grounded and ungrounded PV systems are in widespread use. Even in the United States, where grounded electrical power distribution systems have historically been required, ungrounded PV systems are now permitted, provided a DC disconnect is provided for ungrounded conductors.